Composite structures are used in a wide variety of applications, including in the manufacture of airplanes, spacecraft, rotorcraft and other vehicles and structures, due to their high strength-to-weight ratios, corrosion resistance and other favorable properties. In the aerospace industry, composite structures are used in increasing quantities, for example, to form the wings, tail sections, fuselage and other components, due to their better specific strength and stiffness, which translates to weight savings, which translates into fuel savings and lower operating costs.
As an example, composite aircraft wings may utilize upper and lower outer composite wing skin panels, commonly referred to as “skins,” that are mechanically attached or bonded to an internal frame. The internal frame may typically include reinforcing structures such as spars, ribs and/or stringers to improve the strength and stability of the skins. The skins may be attached to the spars, and the spars provide structural integrity for the wings. In addition, many aircraft wings may be used as fuel tanks (e.g., a fuel tank is defined inside the wing), which may be contained between front and rear spars.
However, composite structures in aircraft do not readily conduct away the extreme electrical currents and electromagnetic forces generated by lightning strikes. Therefore, aircraft with composite structures, such as composite wings, may be equipped with protection against electromagnetic effects (EME) from lighting strikes. For example, conductive media may be provided on a surface to dissipate lightning current away from underlying metal structures and/or fastener systems. In addition, gaps between fastener parts (e.g., two-piece fasteners) and gaps between fastener parts and structural members may be filled with dielectric sealant that provides EME protection. Even if some current is not diverted, the sealant prevents arcing and sparking across the gaps.
However, current EME protection architectures for composite wings are complex and expensive. As an example, the processes of installing the two-piece fasteners and applying the sealant requires extensive manufacturing labor and is performed in confined spaces. For example, the process of manufacturing the wing typically involves match drilling the spars and the skins, removal of the skins from the spars for surface finishing, and realignment of the skins to the spars to close out the wing. Access to the now closed out wing for installation of the fastener parts, installation of other interior systems and injection of the sealant is gained through access holes formed in the lower outer skin, which is inefficient and potentially dangerous for the laborer. Moreover, the sealant adds weight to the aircraft. While the weight added to a single fastener system might seem insignificant, applying the sealant to tens of thousands of fasteners in a single aircraft can add hundreds of pounds.
Accordingly, those skilled in the art continue with research and development efforts in the field of aircraft wings and, in particular, EME compliant wings.